An experimental model was described for inducing spontaneous lymph node metastasis, in which tumor cells of the rat ascites hepatoma AH-109A were transplanted into the subcutaneous tissue of the penis, which is rich of lymph plexus. Growth of tumor at the site of transplantation was measured serially and metastasis was recognized by palpation in the inguinal lymph nodes initially, and then in the axillary and lumbar nodes. When animals were sacrificed 12 days after transplantation, these lymph nodes were weighed and high percentage of metastasis was confirmed by histological examination. As an experimental model of lymph node metastasis, the usefulness of this method was discussed.